Slide-valve fob steam-ewgii



i UNITED STATES PATENT QFFICE.

THOMAS STEVART, OF PHILADELPHIA, PENNSYLVANIA.

SLIDE-VALVE FOR STEAM-ENGINES.

Specification of Letters Patent No. 27,394, dated March 6, 186C.

To all whom it may concern:

i Be it known that I, THOMAS STEWART, of the city and county ofPhiladelphia and State of Pennsylvania, have invented a new and usefulImprovement in Valves for Steam-Engines; and I do hereby declare thefollowing to be a full, clear, and exact description of the same,reference being had to the accompanying drawing and to the letters ofreference marked thereon.

My invention relates to a mode of relieving' the valves of steam enginesfrom that undue pressure of steam which not only detracts from the powerof the engine, but causes great wear of the valve seats and valves andof the appliances used for operating the latter, and my inventionconsists in a yielding' or elastic diaphragm secured to a balance frameand to the interior of the steam chest, and arranged in the mannerdescribed hereafter; so much of its upper or outer surface being exposedto the pressure of steam that while the latter maintains the frame inclose steam tight contact with the valve, the valve is in a greatmeasure relieved from the pressure of steam fully set forth hereafter.

In order to enable others to make and use my invention I will nowproceed to describe the manner in which I apply it to different stylesof valves.

In reference to the accompanying drawing which forms a part of thisspecification Figure l is a sectional view of a steam chest illustratingmy improvement as applied to an ordinary slide valve; Fig. 2, a plan ofFig. l, with the steam chest cover removed; Fig. 3 an inverted plan ofthe balance frame and its yielding diaphragm; Fig. I a modilication ofmy improvement applied to an ordinary slide valve; Fig. 5 my improvementapplied to the steam valve of a Corliss engine and Fig. 6 my improvementapplied to the exhaust valve of the same style of engine.

In reference to Figs. l, 2, and 3, A represents the face of an ordinarysteam cylinder; B its exhaust port, and C and C its two steam ports.

D is the steam chest, E its cover, and Gr the valve having the usualspindle H passing through a stuffing box.

The valve G, which as regards its relations in respect to the ports ofthe cylinder is of the usual construction, has its upper face planedperfectly level and smooth for receiving the balance frame H, which inthis instance is in the form of a box closed on the top by the elasticor yielding diaphragm I, the latter being secured to the top of theframe by means of a square open plate or washer J, and suitable setscrews a a passing through this plate, through the edge of thediaphragm, and screwing into the balance frame so as to form a perfectlysteam tight joint. The diaphragm is secured in the middle by means of aplate j and screw /L to a projection e on the underside of the steamchest cover E, so as to form a steam tight joint at this point. It willbe seen that the diaphragm, between that portion secured to the balanceframe and that part attached to the steam chest coverI is exposed to thepressure of steam within the chest, and that the diaphragm being elasticand at the same time steam-tight it will yield at the exposed points sothat the balance frame can move up and down to a limited extent.

On the introduction of steam into the chest that portion of the area ofthe diaphragm which extends beyond the projection e will be subjected tothe pressure of the steam which consequently maintains the balance-framein such close contact with the upper surface of the valve G, as toprevent the access of steam to the interior of the said balance frame,so that the area of the valve exposed to the direct pressure of thesteam is diminished to an extent equal to the area covered by thebalanceframe. There is however an indirect pressure of steam on thevalve independent of that exerted on the exposed portion of the latter,this indirect pressure being that which forces the balance frame againstthe upper surface of the valve. This .pressure however is notproportionate to the extent of that portion of the diaphragm exposed tothe action of the steam inasmuch as the greater portion of the pressureis resisted by the diaphragm itself and the steam chest cover to whichthe diaphragm is attached and is therefore not communicated to thevalve.

It will be seen without further description that by the above describeddevice the steam valve is relieved from that undue pressure andconsequent friction, which, when the whole area of the valve is exposedto the pressure of steam not only detracts from the powerpf the same butcauses an incessant wear of the valve seat and valve and the appliancesused for operating the latter.

The material which I prefer for using in the diaphragm is wire-clothrendered steam proof by a preparation of gum elastic, although a thinmetal plate may be used to advantage; when the latter is employed it isadvisable to make the plate with a crease on all sides as seen in Fig. iwhich renders the diaphragm more yielding and elastic.

Fig. 5 represents a steam chest and vibrating steam valve and Fig. 6 theexhaust chest and vibrating exhaust valve such as are used on what areWell known to practical engineers as Corliss engines, the valve in bothcases consisting of a cylinder G secured to a spindle K, the cylindersbeing partially cut away at opposite sides as seen in the drawing. .Myimprovement as applied to this class of valves consists in hanging theseat to the inside of the steam chest by means of a yielding diaphragmI, so that the seat H which in this instance is the balance frame may bemaintained in close contact with the curved surface of the valve by thepressure of steam within the chest While at the same time the greaterportion of the area of the seat is unexposed to the pressure of thesteam and the excessive friction of the seat against the valveconsequently obviated. In the exhaust valve, Fig. 6, suliicient of thediaphragm is exposed to the pressure of the exhaust steam to cause theseat or balance frame H to bear With proper eEect on the valve. It willbe readily seen without description or illustration that my improvementmay be applied to what are known as rotary or disk valves.

An orifice may be made in the valve Fig. 1 to carry 0E any waste steamwhich may accidentally gain access to the interior of the balance frame.

I wish it to be understood that I do not claim broadly the elasticdiaphragm I, or the balance frame H, independently of the specificmanner in which they are arranged and applied. But

I claim as my invention and desire to secure by Letters Patent- Theelastic or yielding diaphragm I, attached to the balance frame H and tothe steam chest, and arranged in the manner herein set forth, when thesaid diaphragm has such an extent of its upper surface exposed to thepressure of steam that While the latter maintains the balance frame inclose steam tight contact with the valve, the said valve is relieved ina great measure from the pressure of steam as specified.

In testimony whereof, I have signed my name to this specification, inthe presence of two subscribing witnesses.

Trios. STEWART.

Witnesses HENRY HowsoN, CHARLES D. FREEMAN.

